This invention relates to an air conveyor apparatus for use with generally cylindrical lightweight containers and more particularly to a damperless conveyor which controls the conveying speed of the containers whether en masse or in a sparse or individual flow of containers.
In recent years, air conveyors have become popular for conveying lightweight containers, such as cylindrical lightweight beverage containers, both during the manufacturing of the containers and during the filling operation. Such conveyors have enjoyed considerable success because they allow the conveying of the containers at a much higher speed than was possible with mechanical conveyors. These air conveyors have used, in various forms, air jets and louvers for moving the containers along the conveying surface. The angle at which air is introduced to the conveying surface has included jets or louvers directing the air parallel to the direction of movement as well as various angles transversely to the direction of movement. In general, it has been the intent of these devices to use the blowing force of the air to move the containers in the desired direction.
Also, devices have been developed by the inventor in which air is supplied through air jets in a manner to take advantage of the Coanda Effect to cause the air to move along the surface of the conveyor and therefore along the lower surface of the container on the conveyor. This effect, together with utilizing the Bernoulli Principle, is utilized to create low pressure in the areas at which the air flows at the highest velocity so as to maneuver the containers in response to changes in air pressure rather than relying on the ability of the device to blow the containers in the desired direction. These principles have been used to create desired high and low pressure areas between adjacent containers to regulate their flow.
Barker, U.S. Pat. No. 3,105,720, shows the use of louvers at opposite ends of cylindrical containers for moving them vertically from one conveyor to another.
Futer, U.S. Pat. No. 3,180,688, discloses a mass conveyor which utilizes a series of louvers and vertical jets. The vertical jets suspend the containers above the conveyor while the louvers provide a downstream propelling force for moving the containers in the downstream direction.
Malmgren et al., U.S. Pat. No. 3,385,490, disclose a device for conveying web or sheet material along a conveyor in which louvers are provided which are angled inwardly from the outboard edges of the conveyor toward the center. An exhaust grid is provided at the center of the device for evacuation of air. This device is intended to center a sheet of material and convey it downstream due to the downstream force component of the air passing through the louvers. The inboard component of the air from the louvers is intended to be equal on both sides and therefore center the sheet material over the conveyor.
Fong, U.S. Pat. Nos. 3,733,056 and 4,033,555, each discloses a conveyor for fluidizing particulate material and utilizes louvers pointed in both a downstream direction and a direction substantially transversely to the direction of movement.
Hassan, et al., U.S. Pat. No. 4,165,132, discloses an air conveyor for conveying semiconductor wafers wherein air jets are provided at an inboard angle from the side edges of the conveyor for suspending and centering the wafers over the conveyor. These jets also create a downstream force component which moves the wafer along the conveyor in the downstream direction.
Lenhart, U.S. Pat. No. 4,456,406, discloses a mass conveyor requiring a top cover and utilizes the formation of high pressure areas between containers to form air barriers for the containers to maintain them in a loose separate condition as they move through the conveyor. This is to minimize banging of the containers against each other and potential damage to them due to this banging action.
Lenhart, U.S. Pat. No. 4,732,513, provides a coverless air conveyor in which jets are provided through the conveying surface in a substantially vertical direction with a slight downstream tilt. Side walls are provided to form air dams to create a flowing body of air which enveloped and lifted the respective containers and moved them at a desired speed. However, if any adjustment is desired in the speed of movement of the mass of containers, it is necessary through dampers to vary the volume of air passing through the jets.
All of the foregoing inventions are suitable for their intended purposes. However, in order to control the flow of the containers on the conveyor, it is necessary to provide dampers at various positions along the plenum in order to control the amount of air issuing through the air jets or louvers of any particular location along the conveying surface. This is necessary in order to change the speed of the movement of the containers from one portion of the conveyor to the next to minimize potential damage to the containers as they move from one operative station to another. When using dampers in an effort to control the speed of a container, as the static pressure is varied upward and downward, the velocity from the deck louvers varies accordingly, and as the velocity varies the volume also varies. This makes control very difficult because of the two parallel variables. If the pressure is set too low in an attempt to slow the speed of the container, the container will not be levitated sufficiently above the deck surface and cannot be conveyed. Conversely, if the pressure is set too high, in order to convey the container at the higher speed, the container will be levitated too high above the deck and may wobble, so that it does not flow smoothly down the air conveyor and may tip over, creating a jam along the conveyor.
Furthermore, with the mass air conveyors discussed above, as a container moves from an upstream location to a downstream location, the volume of air acting on each container increases thereby tending to move the containers at greater and greater speeds, toward a terminal velocity. This is particularly true with single or sparse containers moving along the conveyor. Such a condition can result in containers striking each other with sufficient force to cause damage to fragile containers, such as beverage containers.
In accordance with the present invention, a damperless, controlled speed, coverless isometric air conveyor and method for controlling containers en masse at a controlled speed is provided. The term xe2x80x9cisometricxe2x80x9d as used herein means and refers to opposing air volumes creating opposed force vectors along the upper surface of the deck of the conveyor. The term xe2x80x9clouverxe2x80x9d, as used herein, includes any opening through the deck of the conveyor which directs air along or across the conveyor. A first set of louvers extend through the conveyor surface in a downstream direction at an incline to the conveying surface so that the air passing through the louvers has a downstream force vector of a first magnitude. A second set of louvers extend through the conveyor surface in an upstream direction at an incline to the conveying surface so that the air passing through the louvers has a upstream force vector of a second magnitude which is less than the first magnitude thereby creating a vector force differential in the downstream direction to cause movement of the containers in the downstream direction. The louvers along each edge of the conveying surface may be angled in the inboard direction to cause a cross flow of air which tends to bunch a mass of containers in the center portion of the conveyor in a tight pack and provide an additional downstream force component to move the containers in the downstream direction. Additionally, the angled louvers create an air barrier through which the containers must move, thereby being particularly effective for limiting the speed of single or sparse containers that are normally difficult to control. The inboard cross flow of air also creates a low pressure drafting effect at the trailing edge of the containers to assist in maintaining them in an upright position.
More specifically, according to one conceptual view of the louver arrangement, a first set of longitudinally extending louvers is arranged in alternating arrangement with a second set of longitudinally extending louvers wherein an outboard row of longitudinally extending louvers on each side of the deck or conveying surface is always part of the first set. This assures that there is at least one more row of louvers in the downstream direction than in the upstream direction.
Alternatively, multiple rows of longitudinally extending louvers in the downstream direction can be provided with longitudinally extending upstream louvers interspaced therebetween. Also, at least the first outboard row of downstream longitudinally extending louvers can be angled in the inboard direction to provide air flowing transversely of the direction of movement of the containers to create an air barrier to impede movement of single or sparse flow of containers. However, when the conveyor is full of containers the longitudinally extending louvers will all be substantially covered so that the only flow of air is against the bottom of the containers to move them en masse in the desired downstream direction due to the net downstream force vector.
The rows of longitudinally extending louvers have been defined as longitudinally traversing the conveyor surface; however, the rows of louvers can also be defined as traversing laterally across the conveyor surface because of their symmetrical arrangement on the conveyor surface. That is, depending upon the conceptual view taken, the first and second sets of louvers can be defined as arrangements of either laterally or longitudinally extending rows that traverse the conveyor surface.
By varying either the number of downstream louvers with respect to the upstream louvers, by varying the angle of the incline of the louvers with respect to the conveyor surface, or by varying the size of the individual louver openings, a very precise flow of containers can be obtained without the need to vary static air pressure in the plenum or to provide dampers at various incremental locations within the plenum. Also, depending upon the size of the containers and the spacing of the louvers, the use of both downstream and upstream louvers enables air contacting the containers at any location between an upstream location and a downstream location along the conveyor to move them at a substantially constant speed because of a uniform volume of air communicating with them. The speed of the containers is determined by the differential air volume in the downstream direction relative to the upstream air volume. With this construction, containers such as cylinders open at one end and lightweight containers such as STYROFOAM(copyright) plates can be conveyed without loss of control.
When conveying single or sparse containers, the xe2x80x9cfootprintxe2x80x9d or area covered by the bottom of each container in comparison with the louver arrangement is an important consideration for uniform and stable levitation of the containers above the conveyor surface to minimize wobbling. The area covered by the container must be such that both the upstream and downstream louvers are positioned under the bottom of each container regardless of its position on the conveyor surface. Since there are more downstream louvers than upstream louvers, there will be a net downstream air flow under each container bottom.
Additional advantages of this invention will become apparent from the description which follows, taken in conjunction with the accompanying drawings.